This invention relates to solenoids and, more particularly, to a solenoid actuator having a long stroke.
Solenoids are employed as actuators in many different fields of industry. A typical solenoid comprises an electric coil, a sleeve of permeable material surrounding the coil and covering one end thereof, leaving the other end thereof open, and a plunger or core of permeable material lying inside the coil. When the solenoid is unenergized, the plunger is biased by a spring or other similar means so as to protrude from the open end of the coil, leaving an air gap between the plunger and the closed end of the coil. When the solenoid is energized by connecting a source of electrical energy to the coil, there is induced around the coil a magnetic field that draws the plunger into the coil and reduces the air gap.
An important operating characteristic of a solenoid is its stroke, i.e., the distance of travel of the plunger when the solenoid is energized, as depicted by a graph of force on the plunger versus displacement of the plunger from its energized position. Due to the variable air gap in the described conventional solenoid, the force exerted on its plunger decreases rapidly with displacement and, accordingly, its stroke is very limited.